As preservation of environments in addition to energy saving has particularly been required in recent years, development of a technique for achieving higher fuel efficiency of a vehicle has become an important issue. As decrease in a rolling resistance of a tire represents one requirement for fuel efficiency, various studies have been conducted in the field of the art.
Regarding a technique for achieving higher fuel efficiency in connection with a sidewall of a tire, decrease in an amount of a reinforcing agent such as carbon black blended in the sidewall or use of carbon black having a large particle size is most effective. In many cases, however, such measures lead to lower physical properties representative of hardness, such as hardness or modulus, of a mixture of rubber. Namely, when a tire is attached to a car and used, resistance to flaw lowers.
Japanese Patent Laying-Open No. 2004-106796 discloses a rubber composition containing polybutadiene rubber including a large amount of a linear component, as a rubber composition for sidewall for a tire for a passenger car that can achieve lower rolling resistance of a tire.
Japanese Patent Laying-Open No. 2006-063143 discloses a rubber composition containing polybutadiene rubber including 1,2-syndiotactic polybutadiene crystals and tin-modified polybutadiene rubber, as a rubber composition achieving both cut resistance and high fuel efficiency.
Meanwhile, a rubber composition capable of achieving both high fuel efficiency and improved appearance has been desired.